How dynamic visual field dependence–independence interacts with the visual contribution to postural control

Abstract

The present study addresses the question of the links between visual perceptual dependence–independence and the visual contribution to postural control. In our differential approach, the effects of both static and dynamic visual cues on body posture (orientation and stabilisation) and the cognitive spatial orientation (subjective visual vertical) were considered and compared. In this view, nine dependent (DFD) and nine independent (DFI) male subjects with respect to dynamic visual field were selected on the basis of their score in the so-called rod and disc test (RDT). These subjects have also been subjected to the rod and frame Test (RFT), in order to establish their static visual field dependence–independence. In the postural test, the subjects were instructed to stand in the sharpened Romberg position in darkness and under normal or stroboscopic illumination, in front of either a vertical or a tilted frame. Lateral head and body orientation and stability were measured. The hypothesis is that the DFD subjects use mainly visual cues for estimating not only their subjective vertical but also their body orientation and stability. Moreover, we have postulated that these subjects use mainly dynamic visual cues to control balance. The main results are: (1) A strong correlation ( r=0.64) between the dependence–independence with respect to static and dynamic visual field. (2) A slight body lean towards the tilted frame (postural frame effect) in both DFD and DFI subjects, mainly induced by static visual cues. This effect, however, was greater in the DFD subjects. Moreover, dynamic field dependence was correlated with the postural frame effect in continuous vision. (3) DFD subjects were generally much less stable than DFI subjects. (4) In DFD subjects, the improvement of postural stability required mainly the use of dynamic visual cues, for the most part extracted from the vertical frame. DFI subjects were the only ones to be able to improve their stability by means of static visual cues. Moreover, postural performances were correlated with both dynamic and static field dependence. These results clearly show complex interactions between the perceptive styles and the visual contribution to postural control, which largely contribute to the between-subjects variability in balance skills.